This invention concerns a method to obtain vibrations in the walls of the crystalliser of an ingot mould by means of actuators, and also the relative device.
The invention is applied in the field of continuous casting of billets, blooms or slabs of any type or section, in order to reduce friction between the cast product and the walls of the crystalliser, thus allowing the casting speed to be increased and reducing the risk of break-out in the skin of the product being formed.
The crystallisers to which the invention can be applied are those which have a thick wall, or a medium wall or a thin wall, and also those for slabs with short, movable walls so as to vary the width of the slab.
The state of the art covers attempts to reduce the force required to extract the cast product from inside the crystalliser, and the problems connected thereto.
For it is well-known that the skin as it solidifies, at least in the upper part of the crystalliser, tends to stick to the walls, generating considerable friction during the extraction step.
In order to facilitate the separation of the skin from the walls, the state of the art includes generating vertical, mechanical oscillations on the ingot mould which facilitate the extraction of the product and thus make it possible to increase the casting speed and improve the surface quality of the product leaving the crystalliser.
It is also well-known that in the lower part of the crystalliser the skin, which has by now already solidified, tends to separate from the walls, creating an air gap which causes a reduction in the heat exchange between the cooled wall and the solidified skin and therefore a reduction in the flow of heat removed from the molten metal through the wall of the crystalliser.
The present applicants, in their application for a European patent EP-A-0686445, described the use of a crystalliser with thin walls associated with a method to control the deformations of the walls; in this invention, the pressure of the cooling fluid flowing in the transit channel adjacent to the said walls is regulated to compensate for the different shrinkage of the skin of the cast product along the crystalliser according to the type of steel and the casting speed.
According to this document, the walls of the crystalliser take on an elastic quality depending on the different pressures of the cooling liquid flowing inside them, in such a way that, in the first segment of the crystalliser, the negative taper induced by the thermal field is cancelled, and, in the lower part of the crystalliser, the air gap created between the solidified skin and the walls is minimised.
These pressures are calculated in such a way as to obtain the desired deformation of the walls and are maintained substantially constant until the casting parameters are changed, particularly the type of steel and the casting speed.